Method of making magnetic cores



Junejl, 1965 J. I. METZGER, JR 3,186,056

METHOD OF MAKING MAGNETIC CORES Filed Dec. 11, 1961 2 Sheets-Sheet lMoan/rat.

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June 1, 1965 J, 1. METZGER, JR

METHOD OF MAKING MAGNETIC CORES 2 Sheets-Sheet 2 Filed Dec. 11, 1961FIG.5

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United States Patent '0 3,186,066 METHOD F MAKING MAGNETIC CORES JamesI. Metzger, Jr., St. Louis, Mo., assignor to Wagner ElectricCorporation, St. Louis, Mo., a corporation of Delaware Filed Dec. 11,1961, Ser. No. 158,208 3 Claims. (Cl. 29-15557) The present inventionrelates to a method of making magnetic cores. More particularly, thepresent invention relates to an improved method of making curved orwound-type magnetic cores from magnetic strip material.

Curved or Wound-type magnetic cores are usually formed by flatwisebending and assembling magnetic strip material to form an assembly ofnested layers such as by Winding magnetic strip material onto a mandrelto form a coil. The strip material may be wound into a coil havingapproximately the same size and shape it is to have in the finallyassembled apparatus, or it may be wound into a coil which must be formedto the desired shape. The coil is then annealed in the well-known mannerto relieve stresses in the strip material and impart a permanent setthereto. The annealed coil is subsequently assembled with a conductiveWinding structure to form a finished core.

As is well known to those skilled in the art, it is usually necessary inthe manufacture of curved cores to provide spaces or a certain degree oflooseness between turns in a portion of the annealed coil prior to itsas sembly with a conductive winding structure. Such looseness permitsthe annealed coil to be assembled with the conductive winding structurewithout inducing excessive stresses in the magnetic material. Forexample, where an annealed coil is to be unwound and successive portionslinked with a winding structure to form a finished core, theabovementioned looseness of turns is needed so that each of the turns inthe finished core has substantially the same size, shape, and positionit had in the annealed coil and Without having excessive stresses inmagnetic material. Also, in cores having butt joints, such loosenesspermits the tight closing of the joints during assembly.

Various well-known forms of spacer means have been employed and theseinclude metal shims, powder, and burnable materials such as string andpaper. The use cost of material and handling, as well as additionalstorage space. Also, the use of burnable spacer means such as string orpaper often results in contamination of the atmosphere by fumes or burntparticles about the annealing oven or at other work stations where the'coil is handled. There is also danger in the case of liquid dielectricsubmerged induction apparatus of the contamination of the liquiddielectric by such burnt particles unless great care is taken. a

In accordance with the present invention, the use 0 the abovementionedspacer means in the manufacture of magnetic cores is not required andthe abovementioned disadvantages can be avoided. In accordance with oneaspect of the present invention, an improved method of making a magneticcore is provided which includes the steps of forming deformations inmagnetic material,

assembling the strip material into an assembly of nested layers havingspaces between layers-in a portion of the I assembly as a result of thedeformations, and substantially removing the deformations in thematerial in that portion of the assembly to provide the desired spacesor looseness between layers in another portion of the assembly. a I Itis therefore an object of the present mvention to provide an improvedmethod of making a magnetic core I of the abovementioned spacer meansrequires additional wherein the abovementioned disadvantages ofemploying separate spacer means can be avoided.

Another object is to provide a new and improved method of making acurved magnetic core without the necessity of employing separate spacermeans and wherein undesirable stresses in the core material are avoided.

Still another object is to provide a new and improved method of making anon-circular Wound-type magnetic core, which method is relatively simpleand efiicient.

Still another object is to provide an improved method of making agenerally rectangular wound-type magnetic core without the necessity ofemploying separate spacer means and wherein the core produced therebyhas a relatively high space factor.

These and other objects and advantages of the present invention willbecome apparent from the following description and accompanying drawingsin which:

FIG. 1 is a diagrammatic elevational view illustrating the processing ofmagnetic strip material and the winding thereof into a coil,

FIG. 2 is a fragmentary perspective view of the magnetic strip materialindicated at 10a in FIG. 1,

FIG. 3 is a front elevational view illustrating a coil of strip materialformed in the manner shown in FIG. 1, and in position for annealing,

FIG. 4 is a front elevational view of the coil of strip material shownin FIG. 3, but after it has been annealed,

FIG. 5 is a view illustrating a step in one method of linking anannealed coil of strip material with a preformed winding,

FIG. 6 is a cross-sectional view of a preformed winding linked by amagnetic core made in accordance with the present invention,

FIG. 7 illustrates a modified manner of annealing a coil of stripmaterial, and

FIG. 8 illustrates a coil annealed in the manner indicated in FIG. 7.

Referring now to the drawings and particularly to FIGS. 1 and 2,magnetic strip material 10, such as grain oriented silicon steel strip,is first processed and thereafter successive portions are flatwisecurved or bent and assembled together in nested relation. As shown, themagnetic strip material 10 is provided with deformations as it is drawnfrom a supply spool 14 by passing it through a metal forming mechanism15 which is shown as including a pair of similar deforming rollers 16and 18 mounted for rotation on a standard 20 fixed to a base or floor22. Preferably, the strip material 10 is passed between the rollers 16and 18 as it is wound onto a mandrel 24 supported for rotation by astandard 26 fixedly mounted to the base 22. As indicated by the arrowsin FIG. 1, mandrel 24 is rotatable in a clockwise direction by anysuitable-driving meanswhile the two rollers 16 and 18 are rotated inopposite directions with respect to each other as the strip materialpasses therebetween.

The rollers are preferably rotated by the strip material itself asthematerial is wound onto the mandrel, although the rollers may be drivenby auxiliary driving means which may be synchronized with the rotationof the mandrel.- e

valley-like depressions 34.. The strip material is thus shown undulatedor corrugated by the rollers 16..and

. embodiment.

18,'the undulations orcorrugations being exaggerated in the drawing forclarity of illustration. The bosses 32 extend outwardly of the plane ofthe strip material and entirely across the width of the strip in theillustrated Preferably, the metal forming mechanism 15 imparts similarequally spaced bosses or continuous undulations substantially throughoutall of the strip material used in making a magnetic core.

The mandrel '24 is shown generally rectangular in shape and has an outerperiphery which, in this case, substantially defines the inner peripherythat the finished core is to have. The thus far processed strip materiala is flatwise spirally wound around the mandrel until the a desiredamount of material has been transferred'thereto.

The wound coil of corrugated strip and mandrel 24 may then be removedfrom the standard 26. In order to prevent unwinding of the coil,suitable retaining means turns of the coil, these spacesbeingindicatedat '36. In

forming the corrugated strip material 10a around 'the mandrel it has atendency to flatten out, especially as it is bent aroundthe corners andthe opposite short ends of the mandrel. Thus, the spaces 36 betweenturns will be substantially greater in the-opposite longer sides or legs38 and 40 than in the opposite short sides or ends 42 and 44.

The coil of corrugated strip material, as seen in FIG. 3, may now befurther processed to remove the corrugations or bosses, as well asspaces 36 between layers in the longer sides thereof, to thereby providethe desired looseness or space between turns at the ends or corners ofthe coilf This may be done by applying opposing forces to the oppositelonger sides of the coil to flatten the layers in the sides, forexample, vby placing the coil, while on the mandrel, in a press tocompress the coil sides, and then annealing thecompressed coil.

' However, the corrugations and spaces between layers in the sides ofthe coil are preferablyremoved with the corrugated strip material at atemperature sutficient to soften the material, and this is preferablyaccomplished during the strain-relief annealing treatment. The-woundcoil of corrugated strip material 10a on mandrel 24' is preferablyannealed with one of its longer sides above the other as illustrated inFIG. 3. As shown, the longitudinal axis of the coil, which is indicatedby a broken line 46, is parallel to a horizontal base 48, while" thetransverse axis, indicated by a broken line 49, is normal to the base.The base 48 may be a steel supporting plate used to transport the coilinto an annealing oven, the base being disposed in the oven horizontallyor parallel to the floor of the oven. The coil of strip material isannealed byheating it to a suitable temperature which may be about 1600"F.

The coil is under compression in the annealing oven due to the force ofgravity acting on the mass thereof.

In addition to the weight of the strip material in the coil,

any additional forces, such as the weight of a. compression plate 50and/or any other compressive force applied thereto, will, of course,contribute to the total compressive force'acting' on the coil. Dependingon the size of the coils, a suitable number of such wound coils may beplaced in the annealing oven together, each. in the position shown inFIG. 3. .These coils may be disposed in rows with coils in each rowstacked one upon the other. 7

During the annealing process, the strip material becomes supple and thedeformations and spaces between the layers in the sides 38 and 40 arereadily removed as the layers are flattened and forced relativelytightly against one another in the sides due to the forces of gravity.The coil after it has beenysuitably'annealed is illustrated in FIG. 4.It is seen that the layers of strip material in the longer sides of theannealed generally rectangular coil are straight and in close contactengagement with one another and with the longer sides tightly againstthe mandrel. The spaces 36, which were present in the longer sides 38and 40 before annealing, as shown in FIG. 3, are absent after annealing,as shown in FIG. 4. It will be noted however, that there are suitablespaces 51 between layers at the short ends and adjacent the corners ofthe coil. The spaces 51 are principally a result of the removal of spacefrom the sides of the coil during annealing. Thus, supporting the coilin the annealing oven under compression or with pressure on the sidesremoves the deformations in the strip material and effects the transferof spaces from the sides to the ends and corners of the coil.

Because the corrugations or bosses 32 in the strip material 10a in thepreferred embodiment extend across the full width of the material, theforming thereof does not undesirably stress or tear the material, andsuch corrugations are subsequently readily removed.

While a particular pre-winding processing of magnetic strip material hasbeen shown in the drawings by way of illustration, it will be apparentto those skilled in the art that other forms of deformations and methodsof forming them may be employed. For example,

" spacing of assembled layers.

As previously mentioned herein, by providing suitable spaces betweenlayers'in the ends or adjacent the corners of the annealed coil, such asspaces 51 in FIG.

4, the coil can be readily assembled with an inductive winding structurewithout introducing undesirable stresses therein. 7

The annealed coil, after it is removed from the annealing oven andcooled, may be linked with a preformed winding structure, in accordancewith one method, by first unwinding the coil and cutting through thestrip material at spaced intervals toprovide a plurality of sections.FIG. 5 shows a plurality of nested sections 52, 54 and 56, each sectionhaving a length equal to approximately two turns of the coil. Thesesections of strip material may then be linked with an insulatedconductive winding structure, such as indicated at 58 in FIG. 6. Thewinding structure 58 represents a winding structure of a transformer andincludes a pre-formed primary winding 60 and a divided pre-formedsecondary winding 62, the windings forming a window- 64. The sections ofstrip material, starting with the innermost section 52, are successivelythreaded through the window 64 of the winding structure, each beingcollapsed around closed magnetic core having turns substantially thesame size, shape, andrelative position as they had in the annealed coil.In this instance, the core has a plurality of butt joints 66 bridged byan adjacent unbroken layer. The winding structure shown in FIG. 6 islinked by two such cores, one being shown in phantom.

Because of the looseness or space between turns in the annealed coilshown in FIG. 4, the abovementioned steps of unwinding the coil andthreading the successive sections thereof through the window of thewindingstructure can be accomplished without inducing excessive stressesin the strip material. Also, the resulting core will have tight buttjoints and the lamination layers in same manner as the pre-annealed coilof corrugated strip material shown in FIG. 3, and like referencenumerals are used in the drawings to denote like parts. In FIG. 7, thecoil is provided with restraining means for limiting its lengthwisedimension, which dimension is along the longitudinal axis 46, during thesubsequent processing of the coil. As shown in FIG. 7, a rectangularframe or clamp 70 extends around the center of the coil and encirclesthe opposite short ends thereof. The frame 70 includes two oppositeparallel metal side plates 72 (one shown) and two opposite metal endplates 74, the plates being connected at their ends such as by Welding.The side plates 72 extend parallel to the longitudinal axis 46 andmaintain the end plates 74 in fixed relation to each other.

The coil may then be annealed with the longer sides of the coil underpressure such as by placing the coil in the annealing oven while in theposition shown in FIG. 7, which is the same coil position previouslydescribed in connection with FIG. 3. During annealing, as strip materialsoftens, the compressive forces resulting from the force of gravityeffects the removal of the corrugations in the strip material and thetransfer of strip material and spaces from the longer sides to thecorners and ends of the coil. In this case, however, since the framelimits the lengthwise dimension, the resulting annealed coil has aconfiguration which more closely approaches a true rectangle. Theannealed coil is illustrated in FIG. 8, and as seen therein, hassubstantially straight ends, indicated at 76 and 78, with the desiredspaces indicated at 80 be tween layers at or adjacent each of thecorners of the coil.

By limiting or restraining the lengthwise dimension of a coil havingspaces between layers in the sides thereof, such as by frame 70, theover-all length of the core will be somewhat shorter and the spacefactor will be high. Various types of frames for this purpose are, ofcourse, possible. For example, in some cases a pair of end plates, suchas plates 74, may be clamped against their respective coil ends by oneor more surrounding conventional banding straps. Also, where a number ofcoils are placed in the annealing oven together, such restraining meansmay conveniently include a plurality of frames, such as shown in FIG. 7,connected together.

The annealed coil shown in FIG. 8 may be linked with a conductivewinding structure in any suitable manner. For example, this annealedcoil may be assembled with a conductive winding in the manner previouslydescribed in connection with the coil shown in FIG. 4.

While the invention has been described in detail, it is to be understoodthat the description is intended as illustrative rather than limiting asvarious modifications are possible within the scope of the inventionwhich is defined in the appended claims.

What is claimed is:

1. The method of making a wound type magnetic core from a strip ofmagnetic material having a predetermined length and thickness and awidth greater than the thickness thereof, said strip being defined inthickness by a pair of opposed surfaces and in width by a pair ofopposed side edges which respectively intersect with said surfaces,comprising the steps of forming a plurality of spaced ridges eachcontinuously extending entirely across the Width of said strip andsubstantially normal to said side edges to predeterminately shorten thelength of said strip and prevent deleterious stretching of said strip ina direction substantially normal to said surfaces,

winding the shortened length of strip into a closed coil having aplurality of superposed layers of said strip, said coil having opposedside and end portions with adjacent superposed layers in at least oneside por-.

tially remove said ridges fromthe adjacent superposed layers thereof bythe force of gravity and lengthen said adjacent superposed layersthereof to predeterminately provide spacing between adjacent superposedlayers in another portion of the coil, uncoiling the strip from saidannealed coil and cutting the strip into a plurality of sections,

and subsequently assembling said sections with an inductive winding toform said magnetic core.

2. The method of making a wound type magnetic core for a preformedinductive winding from a strip of magnetic material having apredetermined length and thickness and a width greater than thethickness thereof, said strip being defined in thickness by a pair ofopposed surfaces and in width by a pair of opposed side edges whichrespectively intersect with said surfaces, comprising the steps oftransversely bending said strip successively in different directions toproduce a plurality of parallel alternating ridges and valleyssubstantially throughout the entire length of said strip with eachextending substantially normal to said side edges continuously acrossthe entire width of said strip to predeterminately shorten said stripand prevent deleterious stretching of said strip,

winding the shortened strip onto a mandrel to form an oblong generallyrectangular closed coil having -a plurality of superposed layers of saidstrip, the coil having opposed relatively long sides and opposedrelatively short ends with substantially all of the layers in at leastsaid opposed sides spaced from each other by said ridges and valleys,

annealing the coil by positioning said coil While on the mandrel in anannealing oven on one of said sides with the other of said sides abovesaid one side, and Weighting said other side, so that said ridges andvalleys are substantially removed and the layers in said sides arelengthened by the force of gravity while in the oven to provide spacingbetween layers in said ends of the coil,

unwinding said annealed strip from the mandrel,

and reassembling the annealed strip into a coil sur rounding a portionof a preformed inductive winding to form said magnetic core. 3. Themethod of making a wound type magnetic core from a strip of magneticmaterial having a predetermined length and thickness and a width greaterthan the thickness thereof, said strip being defined in thickness by apair of opposed surfaces and in width by a pair of opposed side edgeswhich respectively intersect with said surfaces, comprising the steps offorming a plurality of alternating ridges and valleys in said strip eachextending normal to said side edges and continuously across the entirewidth thereof to predeterminately shorten the length of said strip andprevent deleterious stretching of said strip in a direction normal tosaid surfaces,

winding the shortened strip onto a rotating generally rectangularmandrel to form a closed coil of a plurality of superposed layers ofsaid strip having opposed sides and opposed ends with the layers in saidsides of said coil spaced from each other by said ridges and valleys butwith said ridges and valleys in the strip at the corners of the coilbeing substantially removed as a result of bending the strip around thecorners of the mandrel during the winding of the strip thereon,

. annealing said coil by supporting said coil and mandrel in anannealing oven on one of its sides with the other side above said oneside and with restraining means adjacent the ends of the coil to preventlayers in the ends of the coil from moving away from the mandrel so thatsaid ridges and valleys are substantially removed and the layers in saidsides are lengthened while in the oven by the 'force'of gravity toprovide spacing between layers at-the corners of the coil,

' removing the c'oil'and mandrel from the annealing oven anduncoilingthe annealed strip from the mandrel, and reasseinbling theannealed strip around a portion of a preformed inductive winding to formraj-magnetic core having substantially straight'opposedsides and ends.

7 i s References'Cited by'th'e Exa'miher UNITED STATES PATENTS 705,9357/02 Lee et a1. 336-213 X 2,305,650 12/42 Vienneau 29-15557 2,907,96710/59 Smith 29-15557 X 2,969,585 1/61 Smith 29-15557 3,027,628 4/62 Wilket a1. 29-155.57

JOHN F. CAMPBELL, Primary Examiner.

2. THE METHOD OF MAKING A WOUND TYPE MAGNETIC CORE FOR A PREFORMEDINDUCTIVE WINDING FROM A STRIP OF MAGNETIC MATERIAL HAVING APREDETERMINED LENGTH AND THICKNESS AND A WIDTH GREATER THAN THETHICKNESS THEREOF, SAID STRIP BEING DEFINED IN THICKNESS BY A PAIR OFOPPOSED SURFACES AND IN WIDTH BY A PAIR OF OPPOSED SIDE EDGES WHICHRESPECTIVELY INTERSECT WITH SAID SURFACES, COMPRISING THE STEPS OFTRANSVERSELY BENDING SAID STRIP SUCCESSIVELY IN DIFFERENT DIRECTIONS TOPRODUCE A PLURALITY OF PARALLEL ALTERNATING RIDGES AND VALLEYSSUBSTANTIALLY THROUGHOUT THE ENTIRE LENGTH OF SAID STRIP WITH EACHEXTENDING SUBSTANTIALLY NORMAL TO SAID SIDE EDGES CONTINUOUSLY ACROSSTHE ENTIRE WIDTH OF SAID STRIP TO PREDETERMINATELY SHORTEN SAID STRIPAND PREVENT DELETERIOUS STRETCHING OF SAID STRIP, WINDING THE SHORTENEDSTRIP ONTO A MANDREL TO FORM AN OBLONG GENERALLY RECTANGULAR CLOSED COILHAVING A PLURALITY OF SUPERPOSED LAYERS OF SAID STRIP, THE COIL HAVINGOPPOSED RELATIVELY LONG SIDES AND OPPOSED RELATIVELY SHORT ENDS WITHSUBSTANTIALLY ALL OF THE LAYERS IN AT LEAST SAID OPPOSED SIDES SPACEDFROM EACH OTHER BY SAID RIDGES AND VALLEYS, ANNEALING THE COIL BYPOSITIONING SAID COIL WHILE ON THE MANDREL IN AN ANNEALING OVEN ON ONEOF SAID SIDES WITH THE OTHER OF SAID SIDES ABOVE SAID ONE SIDE, ANDWEIGHTING SAID OTHER SIDE, SO THAT SAID RIDGES AND VALLEYS ARESUBSTANTIALLY REMOVED AND THE LAYERS IN SAID SIDES ARE LENGTHENED BY THEFORCE OF GRAVITY WHILE IN THE OVEN TO PROVIDE SPACING BETWEEN LAYERS INSAID ENDS OF THE COIL, UNWINDING SAID ANNEALED STRIP FROM THE MANDREL,AND REASSEMBLING THE ANNEALED STRIP INTO COIL SURROUNDING A PORTION OF APREFORMED INDUCTIVE WINDING TO FORM SAID MAGNETIC CORE.